1. Field of the Invention
The invention is directed to X-ray fluorescence systems and methods. More particularly, the invention is directed to microscopic X-ray fluorescence with focused X-ray beams.
2. Background Information
Most, if not all atomic elements will fluoresce when illuminated with X-ray energy. The resulting fluorescence spectrum is generally characteristic of the element. In the microelectronics manufacturing field, X-ray fluorescence is used to determine both the presence of elements and with appropriate conditions, the concentration of different elements in deposited layers. Under appropriate conditions, it is also possible to determine layer depths in microelectronics devices using X-ray fluorescence.
Quantitative analysis of the resulting X-ray fluorescence is frequently performed with a technique called fundamental parameters. Typically, analysis of X-ray fluorescence by the fundamental parameters technique uses the spectrum of fluorescence wavelengths and the relative intensities in that spectrum.
Given the analytic capabilities of X-ray fluorescence, and the decreasing size of features on microelectronics devices, microscopic X-ray fluorescence techniques were developed. However, in contrast to optical methods, X-rays are not easily susceptible to the known techniques of optical refraction using a lens. Thus, for applications where a low level of X-ray energy in a small or focused area is sufficient, systems use a high-power X-ray source and a pin-hole or very small aperture to provide X-ray illumination of the small area. However, this is inefficient and does not allow higher X-ray energy without significant and impractical increases in X-ray power. Therefore, techniques to focus X-rays are advantageous and have been developed. One such technique is the capillary optics technique. However, capillary optics for X-ray systems are known to produce a halo effect. Systems to eliminate or reduce the halo effect of an X-ray focusing system are needed.
The known microscopic X-ray fluorescence systems are less sensitive to low atomic number elements and are unable to detect elements below certain numbers. Systems and methods to detect lower atomic number elements are needed.
As the feature size on microelectronic devices decreases and focused X-ray systems generate smaller X-ray spots, it becomes hard to accurately locate particular features on a sample and then accurately position the focused X-ray spot on that particular feature. Systems and methods to accurately and reliably locate small features and position an X-ray spot on the feature are needed.
When X-ray fluorescence systems translate microelectronics wafers during the testing, it is possible that as a result of irregularities, the sample is not uniform or is improperly mounted and the sample contacts parts of the system. These collisions frequently destroy the sample and may damage or destroy parts of the system. Systems and methods to avoid contact between sample and system are needed.